Cargo handling systems, such as material handling units, are used at airports and other similar locations for transferring pallets and cargo containers a relatively long distance between two locations. Some of these cargo handling systems include a steerable, self-propelled transporter, which is connected to a dolly supported on rollers. An example includes the mobile cargo handling system and method disclosed in U.S. Pat. No. 4,348,150 assigned to FMC Corporation, the disclosure which is hereby incorporated by reference in its entirety.
In these type of units, pallets or cargo containers can be conveyed along a conveyor system having driven balls that are protectable against overloading, such as a conveyor system as disclosed in U.S. Pat. No. 5,261,526, assigned to FMC Corporation, the disclosure of which is hereby incorporated by reference in its entirety. The point of contact between the driving roller and the ball is located at some distance below the horizontal plane through the center of the ball, which distance is smaller than the radius of the ball, and allows aluminum pallets and cargo containers to be transported in a direction toward a cargo hold or other area.
However, depending on the physical location and type of cargo hold or receiving area for the pallets and cargo containers, some conveyor systems do not provide a powered drive the entire distance, and thus, "dead zones" are created. The pallets or cargo containers must pass across ball mats or some other type of rolling element.
Typically in a ball mat, a large number of spherical balls have a small portion of their surface exposed to form a small point of contact for the load. These balls are typically about 30 or 40 millimeters in diameter (about 1.18 to 1.57), which sit inside the deck or platform in the "dead zone." The balls are typically spaced about six inches apart, in accordance with International Air Transport Association (I.A.T.A.) specifications for loading equipment of palletized containers. However, these ball mats have several drawbacks. For example, the continual passing of the pallets and cargo containers across the small point contact of the ball surface damages the bottom of the aluminum pallets and cargo containers. Additionally, contaminants often are pulled into the ball mats causing corrosion. If a ball cannot rotate properly, then it is difficult to spin or shift a pallet or cargo container from side-to-side or roll the pallet or cargo container at an angle. It would then be difficult to match the angle with the applied force. As a result, this could increase operator injuries and cause damage to goods, thus raising operating costs.